It is known that steering columns and particularly steering control shafts may be designed in such a way that, in case of a crash of a motor vehicle in which they are mounted, they may be deformed or telescopically pushed together and thus occupy a reduced space so that they do not put the driver at risk during the crash (“safety steering column”).
German Patent Application publication DE 32 13 462 A1, corresponding to European Patent EP 0 091 671 B1, describes a safety steering column for motor vehicles which includes a rigid steering column section and a tube shaped steering column section having a lattice structure, both steering column sections being made of fiber reinforced plastic material. The fiber reinforced plastic material may be a glass fiber reinforced epoxy resin. In case of a an impact of a motor vehicle including this steering column on an obstacle, the tube part comprising the lattice structure may be compressed so that the functionality of a safety steering column is provided. Due to an integral construction of the rigid steering column section and the tube shaped steering column section, there is, however, no lengthwise adjustability of this safety steering column.
German Patent Application publication DE 10 2009 038 039 A1, corresponding to US Patent Application US 2012/0115621 A1, describes a shaft, particularly an articulated shaft for the power train of a motor vehicle, and a coupling element which is connected to one end of the shaft, both the shaft and the coupling element at least partially consisting of a fiber reinforced plastic material.
Steering columns which completely or partially consist of plastic material or fiber reinforced plastic material are, for example, described in German Patent DE 10 2012 005 434 B3, corresponding to US 2015/0047456 A1, European Patent Application publication EP 0 053 284 A1, corresponding to U.S. Pat. No. 4,465,301 A, and UK Patent Application publication GB 2 017 566.
Two- or multi-part steering columns and steering control shafts which may be telescopically pushed together are, for example, known from German Patent Application publication DE 10 2010 039 253 A1 and German Patent Application publication DD 264 894 A1.
German Patent Application publication DT 23 47 372 A1 describes a form fit connection between two parts with a spline for transferring torque between the two parts. One of the two parts has a guiding surface and teeth which are hardened at their sides facing the guiding surface and which are made as cutting edges. The second part has a counter surface receiving the guiding surface, a counter profile of the second part being cut by the teeth of the first part when pressing the two parts together. Due to this way of cutting of the counter profile, it exactly matches the creating profile of the teeth. For example, a rigid connection of a hollow gear to the interior of a gear housing is provided, in which the hollow gear is neither movable in circumferential nor axial direction.
Canadian Patent Application publication CA 2 067 580 A1 describes a drive shaft made of fiber reinforced plastic to which a metal fitting is connected. At its outer circumference, the fitting is provided with a spline, whereas the drive shaft, at its inner circumference, has a smooth surface. A film, a foil or a layer is applied between the surfaces of the drive shaft and the spline of the fitting. The film, foil or layer may be made of a metal such as iron, copper, nickel, aluminum, titanium, silver, tin, zinc or of an alleys alloy such as brass, of a resin such as polyester resin, polyamide resin, polyimide resin, polycarbonate resin, other artificial resins and mixtures, or of a fiber reinforced resin such as a glass fiber mat impregnated with resin. Teeth of the spline of the fitting do not cut the counter profile into the inner circumference of the drive shaft but press it into the film, the foil or layer. It follows from the nature of a connection between a fitting and a drive shaft that this connection is fixed both for rotation about a longitudinal axis of the drive shaft and for shifts in the direction of this longitudinal axis.
German Patent DE 30 07 896 C2, corresponding to U.S. Pat. No. 4,451,245 A, describes a connection between a fitting made of metal and a hollowshaft made of fiber reinforced plastic material. The fitting has a spline at its outer circumference, which cuts into an inner wall of the hollow shaft when pushing the hollow shaft onto the fitting.
US Patent Application publication US 2014/0059832 A1 discloses a method of manufacturing an intermediate shaft including an internal shaft having an external spline, a tubular external shaft having on an inner circumference thereof an internal spline, and a resin coating provided on the external spline. A central axis line of an internal shaft manufacturing intermediate product and a central axis line of an external shaft manufacturing intermediate product are aligned with each other, and the intermediate products are held in such a way that the central axis lines thereof can be adjusted in a heating adaption step. In this state, the intermediate products slide relative in an axial direction. In the heating adaption step, a grease or lubricant is interposed between the intermediate products.
US Patent Application publication US 2011/034256 A1 discloses a spline telescopic shaft including an inner shaft having an outer tooth surface, and a cylindrical outer shaft having an inner tooth surface and arranged to fit to the inner shaft slidably in an axial direction of the inner shaft. Either one of the outer tooth surface and the inner tooth surface includes a first resin coating. The other of the outer tooth surface and the inner tooth surface includes a second resin coating. The second resin coating is formed by sliding an intermediate member for manufacturing the inner shaft and an intermediate member for manufacturing the outer shaft in the axial direction to transfer a part of a resin material provided in the intermediate member for manufacturing the shaft including the one tooth surface for forming the first resin coating to the intermediate member for manufacturing the shaft including the other tooth surface.
German Utility Model publication DE 20 2010 017 747 U1 discloses a sliding sleeve for supporting a telescopic steering spindle comprising an inner spindle and an outer spindle which are arranged coaxially and movable with regard to each other and which have a cross-section for torque transfer differing from a circular cross-section. An intermediate space between the inner spindle and the outer spindle receives the sliding sleeve containing a thermoplastic material and having an inner surface and an outer surface. The guiding sleeve may be fixed to the inner or to the outer spindle.
In all known cases in which a counter profile in one part is directly cut by a spline provided in another part, the two parts are rigidly connected to each other, and no relative movability of the two parts is desired in any direction.
There still is the need of a lightweight and torsional rigid shaft comprising two parts which may be easily shifted with regard to each other in a direction of a main axis.